Diana suggested we go to Dimond Park in Oakland. Click on the name for a map. The address is 3860 Hanly Rd, Oakland, CA. Phone: (510) 238-2082 Berkeley residents can take Highway 13 to Park Blvd. (west), then make a left on Wellington. The rest of us are better off taking 580 to Park Blv (east), then making a right on Wellington.
Diana says "It's not very far away, has parking and restrooms, and offers an interesting view of a creekbed between two rocky cliffs with some rather picturesque ruins (from bridges)." The park is small enough that if you park on the street you will still be able to find us.